Oesophagus & stomach Flashcards
What layers make up the mucosa layers?
Epithelium
Lamina Propria
Muscularis Mucosae
Assign a number to the lables in the image below
Where does the oseophagus start and end?
Name 3 structures located near by?
Name two structures that are anterior to the oesophagus?
Descending aorta is ……………..and thoracic duct crosses
posterior to oesophagus between ……. and …….
Physiological Anatomy of the Oesophagus
Starts at C5 and ends at T10
Structures located nearby include: trachea, aorta and
diaphragm.
Trachea and pericardium are anterior.
Descending aorta is posterior and thoracic duct crosses
posterior to oesophagus between T7 and T4.
What is the function of the oesophagus?
Function: Conduit for food, drink and swallowed secretions from pharynx to stomach
What is the structure of the epithelium in the oesophagus?
Non-keratinising stratified squamous
What are the functions of the epithelium in the oesophagus?
‘Wear & Tear’ lining
(extremes of temp. & texture)
Lubrication – Mucus secreting glands
(also saliva)
Because the oral cavity leads to two different places (the lungs and the stomach) it is essential that we get food and air getting to their correct destinations.
This is achieved by the ………….. and the …………. ……………… …………….. At rest, the oesophageal sphincter is ……………… active and the epiglottis is in the ……….. position.
What happens to the strucutes which were named above when you swallow?
Because the oral cavity leads to two different places (the lungs and the stomach) it is essential that we get food and air getting to their correct destinations.
This is achieved by the epiglottis and the upper oesophageal sphincter. At rest, the oesophageal sphincter is tonically active and the epiglottis is in the upright position.
These structures move during swallowing, with the epiglottis coming down to cover the entrance to the trachea as the bolus of food moves through the pharynx, and the upper oesophageal sphincter relaxes allowing it to flow into the oesophagus.
What type of muscle is the upper oesophageal sphincter and the lower oesophageal sphincter made out of?
The upper oeaophageal spincter is composed of two muscles:
Name them and state if they have a commonality with circular muscle layer of the GI tract or if it has acommonality with the longitudinal muscle layer?
The oesophagus is approximately 25 cm long in a typical adult male, and its wall is made of a combination of skeletal and smooth muscle. Specifically, the upper oesophagus is composed of …………… muscle only, and the lower oesophagus is …………… muscle only. The middle third is a mixture of the two as the proportion of ……………. muscle tapers along its length.
Despite the involvement of skeletal muscle, it is not under voluntary control.
The upper oeaophageal spincter is composed of two muscles:
Constrictor pharyngeal medius - which has commonality with the circular muscle layer of the GI tract
Constrictor pharynges inferior - which has commonality with the longitudinal muscle layer
The oesophagus is approximately 25 cm long in a typical adult male, and its wall is made of a combination of skeletal and smooth muscle. Specifically, the upper oesophagus is composed of skeletal muscle only, and the lower oesophagus is smooth muscle only. The middle third is a mixture of the two as the proportion of skeletal muscle tapers along its length.
Despite the involvement of skeletal muscle, it is not under voluntary control.
The lower oesophageal sphincter can also be split into two portions:
Name them and describe them?
The oesophagus is under …………….. pressure most of the time, whereas the stomach is under ………………. pressure.
The epithelial lining of the oesophagus is an arrangement of …….-……………… ……………. ………………… cells, which forms a robust wear-and-tear lining to protect the oesophagus from a variety of ingested foods, ranging from smooth to abrasive, hot, cold and acidic. This lining exists all the way to the ……………… ……………. …………………, where the epithelial cells are arranged as ……………… ……………. …………………. This is to address the different conditions these epithelia need to tolerate (i.e. resistance against strong stomach acid). This epithelial change occurs within the sphincter along a jagged line called the………………. .
The lower oesophageal sphincter can also be split into two portions:
The internal component - which is built into the circular smooth muscle of the oesophageal wall
The external component - which is formed by the right crus of the diaphragm (voluntary control)
The oesophagus is under negative pressure most of the time, whereas the stomach is under positive pressure.
The epithelial lining of the oesophagus is an arrangement of non-keratinised stratified squamous cells, which forms a robust wear-and-tear lining to protect the oesophagus from a variety of ingested foods, ranging from smooth to abrasive, hot, cold and acidic. This lining exists all the way to the lower oesophageal sphincter, where the epithelial cells are arranged as simple columnar epithelia. This is to address the different conditions these epithelia need to tolerate (i.e. resistance against strong stomach acid). This epithelial change occurs within the sphincter along a jagged line called the z-line.
What happens in stage 0, 1, 2, 3 of swallowing?
State what happens to the sphincters during each stage?
Swallowing
Swallowing is a highly complex, coordinated event that is initiated by the swallowing centre. A brief summary of the different phases are outlined below.
Stage 0: The oral phase. Chewing and saliva help to prepare the bolus for swallowing. Both oesophageal sphincters are constricted.
Stage 1: The Pharyngeal phase. As the food bolus moves to the back of the pharynx the pharyngeal musculature helps to guide it towards the oesophagus. Both oesophageal sphincters open.
Stage 2: Upper oesophageal phase. The upper sphincter closes, and superior rings of circular muscle contract as inferior rings dilate. Sequential contractions of longitudinal muscle help guide the food down the gullet.
Stage 3: Lower oesophageal phase. As food passes through the lower sphincter that too closes, and the peristaltic wave continues to push food into the stomach.
WHat are the 3 main functions of the stomach?
Digestion of macronutrients: this can be chemical (acid and enzymes) and mechanical (mixing and churning)
Storage reservoir for food: until downstream organs are ready to receive the stomach contents
Immunological protection: Strong acid helps to destroy ingested pathogens
The stomach mucosa is lined with …………. epithelia and it invaginate into …………. ………… which contain specialist exocrine and endocrine cells.
From an anterior perspective, the stomach can be split into ……….. anatomical regions, which each contain different cells in different quantities.
Name the 5 regions the stomach can be split into?
The stomach mucosa is lined with columnar epithelia and it invaginate into gastric pits which contain specialist exocrine and endocrine cells.
From an anterior perspective, the stomach can be split into five anatomical regions, which each contain different cells in different quantities.
What regions of the stomach produce what?
Stomach wall
The wall of the stomach is structurally similar to other parts of the digestive tract, with the exception that ……..
Name the exception and what is this exceptions role?
In the empty state, the stomach is contracted and its ………….. and ……………. are thrown up into folds called ……………. Following consumption of food and fluids, as the volume of the stomach increases, the…………… are stretched and become flat.
The stomach only has a minor role in absorption, so the presence of ………….. (instead of villi) allows the stomach to undertake its ……………… function.
Stomach wall
The wall of the stomach is structurally similar to other parts of the digestive tract, with the exception that the stomach has an extra oblique layer of smooth muscle inside the circular layer, which aids in performance of complex grinding motions (mechanical digestion).
In the empty state, the stomach is contracted and its mucosa and submucosa are thrown up into folds called rugae. Following consumption of food and fluids, as the volume of the stomach increases, the rugae are stretched and become flat.
The stomach only has a minor role in absorption, so the presence of rugae (instead of villi) allows the stomach to undertake its reservoir function.
Stomach-Structure activity Relationship
What does the z line represent?
What type of cells are below the z line and what type of cells are above the z line?
Anatomy of the stomach
The lower oesophageal sphincter (also called the gastrooesophageal sphincter) is in place to allow movement of food and fluids into the stomach, but to ensure that the acidic contents of the stomach remain separate from the vulnerable oesophageal tissue.
The z-line is a visible threshold between epithelia of the oesophagus (stratified squamous cells) and the stomach (simple columnar cells). The oesophageal epithelium is light pink in colour, and functional as a wear and tear lining. The stomach lining is a bright red and more resistant to low pH.
The mucous gel lining of the stomach provides considerable protection against the corrosive acid.
What are the two types of stomach contractions?
What are their functions?
What nervous system does it activate?
Two types of movement (motility) occur in the stomach: peristalsis and segmentation (mixing)
The contractions occur about every 20 seconds and proceed from the body of the stomach toward the pyloric sphincter.
About 20% of the contractions in the stomach are peristaltic waves
Waves of peristalsis begin as gentle muscular contractions near the lower esophageal sphincter and continue down the stomach toward the pyloric sphincter
As the contractile waves near the distal end of the stomach, they become much stronger and more forceful; this results in thoroughly mixed chyme before it passes through the pyloric sphincter
As the peristaltic wave passes through the partly opened pyloric sphincter, it causes the chyme to move through it in a back and forth fashion. This serves to break up the larger materials left in the chyme
About 80% of the contractions in the stomch are segmentation contractions-relatively weak contractions that thoroughly mix ingested food with stomach secretions to form chyme
The more fluid part of the chyme is pushed toward the pyloric sphincter.
The more solid part is pushed back toward the body of the stomach
The neural mechanisms that stimulate stomach secretions also increase stomach motility. The major stimulus is distension (stretching) of the stomach wall
Increased stomach motility increases stomach emptying
What two substances do cheif cells produce?
How is the zymogen produced by cheif ccells activated and where is it activated?
Why is it secreted as a precursor?
Name 4 cellular features of cheif cells?
Cheif Cells
These cells produce a protease zymogen(pepsinogen) and a lipase (gastric lipase). Pepsinogen is activated to pepsin in the presence of HCl in the gastric lumen;
it is secreted as a precursor to prevent it auto digesting the chief cells.
Pepsin then breaks dietary proteins into smaller peptide chains
. Gastric lipase is an enzyme that digests fats by removing a fatty acid from a triglyceride molecule.
Parietal cells
These are the……….-secreting cells of the stomach. They exist in a quiescent (sleeping) state until activated. Then the high number of ……………. in the cytoplasm fuse with the small invaginations on the apical surface to make complicated ……………… surface, with a large surface area for acid secretion.
These cells are rich in mitochondria to provide energy for membrane transport.
The strong HCl has a number of useful functions. List 3
Parietal cells also secrete ………. ……………, a glycoprotein essential for the absorption of ……………… …….. Deficiency in this substance will lead to……………… …………… .
Parietal cells
These are the acid-secreting cells of the stomach. They exist in a quiescent (sleeping) state until activated. Then the high number of tubovesicles in the cytoplasm fuse with the small invaginations on the apical surface to make complicated canalicular surface, with a large surface area for acid secretion.
These cells are rich in mitochondria to provide energy for membrane transport.
The strong HCl has a number of useful functions: 1) to kill ingested pathogens; 2) activate protease zymogens; 3) alter protein structure to help digestion
Parietal cells also secrete intrinsic factor, a glycoprotein essential for the absorption of vitamin B12. Deficiency in this substance will lead to pernicious anaemia.
List 3 cellular features of parietal cells?
Parietal Cell: Resting
Many mitochondria (requires lots of ATP)
Cytoplasmic tubulovesicles (contain H+/K+ ATPase)
Internal canaliculi (extend to apical surface)
Parietal Cell: Secreting
Tubulovesicles fuse with membrane and microvilli project into canaliculi
Mucous cells
Mucous cells are high in number and secrete a ………….-rich mucous which helps to protect the stomach lining. The acidic environment in the lumen of the stomach is very low (pH …-…), however the presence of mucous keeps the pH next to the lining much closer to …. The mucus lining also helps to protect the stomach lining from active …………. and ……….., which may interfere with the lipid bilayer and its membranous transporters.
Mucous cells
Mucous cells are high in number and secrete a bicarbonate-rich mucous which helps to protect the stomach lining. The acidic environment in the lumen of the stomach is very low (pH 2-3), however the presence of mucous keeps the pH next to the lining much closer to 7. The mucus lining also helps to protect the stomach lining from active lipase and proteases, which may interfere with the lipid bilayer and its membranous transporters.
Define enteroendocrine?
Enteroendocrine cells are cells found in the wall of the gut that secrete hormones that regulate numerous processes in the body, including controlling glucose levels, food intake, and stomach emptying
G cells
These are ……………. cells found at the bottom of the ………….. pits. G-cells release the hormone ………….. into the bloodstream in response to ………….. nerve stimulation, the presence of ………….. in the stomach, and stomach …………...
Gastrin travels through the blood to receptor cells in the ………….. where it stimulates ………….. secretion and …………... Stimulation of ………….. ………….. by gastrin leads to stronger contractions of the stomach and the opening of the ………….. ………….. to move food into the duodenum.
Gastrin also binds to receptors on cells in the ………….. and ………….. where it increases the secretion of pancreatic juice and bile.
Gastric pits
The stomach is lined with millions of gastric pits, which are deep pores within the stomach mucosa, which lead to multiple gastric glands, which house the functional secretory cells of stomach. These pits contain a mixture of cells responsible for secreting gastric juice, which is a cocktail of hydrochloric acid, enzymes and enzyme zymogens. Cells in these glands also secrete mucous, paracrine signalling molecules and hormones.
G cells
These are enteroendocrine cells found at the bottom of the gastric pits. G-cells release the hormone gastrin into the bloodstream in response to vagus nerve stimulation, the presence of peptides in the stomach, and stomach distension.
Gastrin travels through the blood to receptor cells in the stomach where it stimulates gastric secretion and motility. Stimulation of smooth muscles by gastrin leads to stronger contractions of the stomach and the opening of the pyloric sphincter to move food into the duodenum.
Gastrin also binds to receptors on cells in the pancreas and gallbladder where it increases the secretion of pancreatic juice and bile.
Name the 3 other cells types of the stomach and state their functions?
Enterochromaffin-like cells (ECL)
These cells are a type of neuroendocrine cell found deep in the gastric glands, usually in the vicinity of parietal cells. They secrete histamine which stimulates the secretion of acid from the parietal cells.
D-cells
These enteroendocrine cells secrete somatostatin, which has a generally inhibitory effect on gastrointestinal function. Within the gastric gland somatostatin inhibits ECL production of histamine and parietal cell activity, both of which inhibit the secretion of hydrochloric acid.
Gastric stem cells
These pluripotent cells are capable of differentiating into all of the different cells of the stomach, under the influence of different factors. The development pathway varies for different parts of the stomach.
State how parietal cells produce gastric acid?
Parietal cells
Carbon dioxide diffuses down its concentration gradient from the blood into the parietal cell and, in the presence of carbonic anhydrase, is combined with water to form carbonic acid, which dissociates into bicarbonate and a proton. The bicarbonate is exchanged with a chlorideion in the interstitial space. This causes chloride ions to move down their concentration gradient into the stomach lumen via chloride channels. To pump the protons into the lumen the cell needs to move potassium from the interstitial space to the lumen. This is achieved via a sodium potassium exchanger in the basolateral membrane, and chloride channels in the apical membrane. Now, potassium can be pumped into the cell in exchange for protons. The potassium then re-enters the lumen through the potassium channels and the secreted proton combines with chloride to form hydrochloric acid.
The activities of the stomach can be split into three distinct phases of activity, list them and for each one fill out the folwing?
Afferent
Efferent
Effect
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